Multi-domain liquid crystal display device

ABSTRACT

A multi-domain liquid crystal display device includes first and second substrates facing each other and a liquid crystal layer between the first and second substrates. A plurality of gate bus lines are arranged in a first direction on the first substrate and a plurality of data bus lines are arranged in a second direction on the first substrate to define a pixel region. A pixel electrode is electrically charged through the data bus line in the pixel region. A common-auxiliary electrode surrounds the pixel electrode on a same layer whereon the gate bus line is formed.

This application is a Continuation-In-Part of application Ser. No.09/250,262, filed Feb. 16, 1999, now U.S. Pat. No. 6,335,776.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device (LCD),and more particularly, to a liquid crystal display device having a sideor auxiliary electrode.

2. Description of the Related Art

Recently, an LCD has been proposed where the liquid crystal is notaligned and the liquid crystal is driven by common-auxiliary electrodesinsulated from pixel electrodes. FIG. 1 is sectional view of pixel unitof the conventional LCDs.

Regarding conventional LCDs, a plurality of gate bus lines arranged in afirst direction on a first substrate and a plurality of data bus linesarranged in a second direction on the first substrate divide the firstsubstrate into a plurality of pixel regions. A thin film transistor(TFT) applies image signal delivered from the data bus line to a pixelelectrode 13 on a passivation layer 37. The TFT is formed on each pixelregion and comprises a gate electrode, a gate insulator, a semiconductorlayer, a source electrode, and a drain electrode, etc. Side electrode 15is formed surrounding the pixel electrode 13 on the gate insulator,thereon passivation layer 37 is formed over the whole first substrate,and a part of pixel electrode 13 overlaps side electrode 15.

Alternatively, pixel electrode 13 is formed on the gate insulator, andpassivation layer 37 is formed over the whole first substrate.

On second substrate, a common electrode 17 is formed and together withpixel electrode 13 applies electric field to a liquid crystal layer.Side electrode 21 and open area (slit) 27 distort the electric fieldapplied to the liquid crystal layer. Then in a unit pixel liquid crystalmolecules are driven variously. This means that when voltage is appliedto the LCD, dielectric energy due to the distorted electric fieldarranges the liquid crystal directors in needed or desired positions.

In the LCDs, however, open area 27 in common electrode 17 or pixelelectrode 13 is necessary, and the liquid crystal molecules could bedriven stably when the open area is wider. If the electrodes do not havean open area or the width of the open area is narrow, the electric fielddistortion needed to divide the pixel region becomes weak. Then, whenvoltage over a threshold voltage, V_(th), is applied, the time needed tostabilize the liquid crystal directors increases. In particular, theresponse time can be over 100 msec. At this time, disclination occursfrom the area where the liquid crystal directors are parallel with atransmittance axis of the polarizer, which results in a decrease inbrightness. Further, according to the surface state of LCDs, the liquidcrystal texture has an irregular structure.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an LCD thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a multi-domain LCDhaving high response time characteristics and high brightness by stablearrangement of liquid crystal molecules.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve the objects and in accordance with the purpose of theinvention, as embodied and broadly described herein, a multi-domainliquid crystal display device comprises first and second substratesfacing each other; a liquid crystal layer between said first and secondsubstrates; a plurality of gate bus lines arranged in a first directionon said first substrate and a plurality of data bus lines arranged in asecond direction on said first substrate to define a pixel region; apixel electrode electrically charged through said data bus line in saidpixel region; a common-auxiliary electrode surrounding said pixelelectrode on a same layer whereon said gate bus line is formed; a gateinsulator over said whole first substrate; a passivation layer on saidgate insulator over said whole first substrate; a light shielding layeron said second substrate; a color filter layer on said light shieldinglayer; a common electrode on said color filter layer; and an alignmentlayer on at least one substrate between said first and secondsubstrates.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of the specification, illustrates embodiments of the invention andtogether with description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a sectional view of the liquid crystal display device in therelated art;

FIGS. 2A, 2B, and 2C, 2D, 2E, 2F, 2G are plan and sectional views of themulti-domain liquid crystal display devices according to the firstembodiment of the present invention;

FIGS. 3A, 3B, and 3C, 3D, 3E, 3F, 3G, 3H are plan and sectional views ofthe multi-domain liquid crystal display devices according to the secondembodiment of the present invention;

FIGS. 4A and 4B, 4C, 4D, 4E, 4F are plan and sectional views of themulti-domain liquid crystal display devices according to the thirdembodiment of the present invention;

FIGS. 5A, 5B and 5C, 5D are plan and sectional views of the multi-domainliquid crystal display devices according to the fourth embodiment of thepresent invention;

FIGS. 6A and 6B are plan and sectional views of the multi-domain liquidcrystal display devices according to the fifth embodiment of the presentinvention;

FIG. 7 is a plan view of the multi-domain liquid crystal display deviceaccording to the sixth embodiment of the present invention;

FIGS. 8A to 8G are plan views showing the various electric fieldinducing windows and dielectric frames according to the embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the multi-domain liquid crystal display device of thepresent invention is explained in detail by accompanying the drawings.

FIGS. 2A and 2B are plan views of the multi-domain liquid crystaldisplay devices according to the first embodiment of the presentinvention, and FIGS. 2C and 2D, 2E, 2F, 2G are sectional views takenalong the lines I-I′ and II-II′ in FIG. 2A.

As shown in the figures, the present invention comprises first andsecond substrates, a plurality of gate bus lines 1 arranged in a firstdirection on a first substrate and a plurality of data bus lines 3arranged in a second direction on the first substrate, acommon-auxiliary electrode 15, a TFT, a passivation layer 37, and apixel electrode 13.

On a second substrate, a light shielding layer 25 is formed to shieldthe light leaked from gate and data bus lines 1, 3, and the TFT, a colorfilter layer 23 is formed on the light shielding layer, a commonelectrode 17 is formed on the color filter layer, and a liquid crystallayer is formed between the first and second substrates.

Data bus lines 3 and gate bus lines 1 divide the first substrate into aplurality of pixel regions. The common-auxiliary electrode distortselectric field on a same layer whereon the gate bus line is formed. TheTFT is formed on each pixel region and comprises a gate electrode 11, agate insulator 35, a semiconductor layer 5, an ohmic contact layer (notshown in the figure), and source/drain electrodes 7, 9. Passivationlayer 37 is formed on the whole first substrate 31. Pixel electrode 13is coupled to drain electrode 9.

To manufacture the multi-domain LCD of the present invention, in eachpixel region on the first substrate, a TFT is formed comprising gateelectrode 11, gate insulator 35, semiconductor layer 5, ohmic contactlayer (not shown in the figure) and source/drain electrodes 7, 9. Atthis time, a plurality of gate bus lines 1 and a plurality of data buslines 3 are formed to divide the first substrate 31 into a plurality ofpixel regions.

Gate electrode 11 and gate bus line 1 are formed by sputtering andpatterning a metal such as Al, Mo, Cr, Ta, Al alloy, etc. At this time,common-auxiliary electrode 15 is formed surrounding the pixel region.The gate insulator 35 is formed by depositing SiN_(x) or SiO_(x) usingPECVD thereon. Semiconductor layer 5 and the ohmic contact layer areformed by depositing with PECVD(Plasma Enhanced Chemical VaporDeposition) and patterning amorphous silicon (a-Si) and doped amorphoussilicon (n₊a-Si), respectively. Also, gate insulator 35, amorphoussilicon (a-Si), and doped amorphous silicon (n₊a-Si) are formed by PECVDand patterned. Data bus line 3 and source/drain electrodes 7, 9 areformed by sputtering and patterning a metal such as Al, Mo, Cr, Ta, Alalloy, etc.

A storage electrode 43 is formed to overlap gate bus line 1 and/orcommon-auxiliary electrode 15 at the same time, the storage electrode 43makes a storage capacitor with gate bus line 1 and/or common-auxiliaryelectrode 15.

Subsequently, passivation layer 37 is formed with BCB(BenzoCycloButene), acrylic resin, polyimide based material, SiN_(x) orSiO_(x) on the whole first substrate. Pixel electrode 13 is formed bysputtering and patterning a metal such as ITO (indium tin oxide). Acontact hole 39 is formed to connect the pixel electrode to the drainand storage electrodes by opening and patterning a part of thepassivation layer on drain electrode 9.

When common-auxiliary electrode 15 and gate bus line 1 are formed withthe same material, the common-auxiliary and gate electrodes aresimultaneously formed with one mask and connected electrically to commonelectrode 17, or it is possible to form them with different materials ordouble layer with additional masks.

On the second substrate 33, a light shielding layer 25 is formed toshield any light leakage from gate and data bus lines 1, 3, the TFT, andcommon-auxiliary electrode 15. A color filter layer 23 is formed R, G, B(red, green, blue) elements to alternate on the light shielding layer. Acommon electrode 17 is formed with ITO on the color filter layer, and aliquid crystal layer is formed by injecting liquid crystal between thefirst and second substrates.

To apply voltage (V_(com)) to common-auxiliary electrode 15, Ag-dottingpart is formed in each corner of driving area on first substrate 31,electric field is applied with second substrate 33, and the liquidcrystal molecules are driven by the potential different. A voltage(V_(com)) is applied to common-auxiliary electrode 15 by connecting theAg-dotting part to the common-auxiliary electrode, which is accomplishedsimultaneously by forming the common-auxiliary electrode.

On at least one substrate, a compensation film 29 is formed withpolymer. The compensation film is a negative uniaxial film, which hasone optical axis, and compensates the phase difference of the directionaccording to viewing-angle. Hence, it is possible to compensateeffectively the right-left viewing-angle by widening the area withoutgray inversion, increasing contrast ratio in an inclined direction, andforming one pixel to multi-domain.

In the present multi-domain liquid crystal display device, it ispossible to form a negative biaxial film as the compensation film, whichhas two optical axes and wider viewing-angle characteristics as comparedwith the negative uniaxial film. The compensation film could be formedon both substrates or on one of them.

After forming the compensation film, polarizer is formed on at least onesubstrate. At this time, the compensation film and polarizer arepreferably composed as one.

In the multi-domain liquid crystal display device in the FIG. 2, pixelelectrode 13 overlaps common-auxiliary electrode 15, light shieldinglayer 25 overlaps the common-auxiliary electrode, and then the apertureratio is improved. Storage electrode 43 forms a storage capacitor CST byoverlapping gate bus line 1. Although not shown in the figures, thestorage electrode 43 may overlap the common-auxiliary electrode 15.

Moreover, the LCD in FIG. 2B has lower short generation in thecommon-auxiliary electrode and gate bus line than that of FIG. 2A. FIG.2D, 2F show that passivation layer 37 includes SiN_(x) or SiO_(x) andFIG. 2E, 2G show that passivation layer 37 includes BCB or acrylic resinin the LCD. Also, FIG. 2D, 2E show that dielectric frame 53 is formed onthe common electrode 17, and FIG. 2F, 2G show that electric fieldinducing window 51 is formed in the common electrode 17.

FIGS. 3A and 3B are plan views of the multi-domain liquid crystaldisplay devices according to the second embodiment of the presentinvention, and FIGS. 3C and 3D are sectional views taken along the linesIII-III′ in FIG. 3B, FIGS. 3E, 3F, 3G, 3H are sectional views takenalong the lines IV′IV′ in FIG. 3A.

Pixel electrode 13 does not overlap common-auxiliary electrode 15, andthe light shielding layer 25 overlaps the pixel electrode 13. At thistime, the gate insulator 35 and the passivation layer 37 on thecommon-auxiliary electrode 15 are removed, which intensifies theelectric field of common-auxiliary electrode 15 that is applied to thepixel electrode 13 (refer to FIG. 3B).

The FIG. 3C shows a portion of the gate insulator 35 and passivationlayer 37 that are removed to expose a part of the common-auxiliaryelectrode 15, and the FIG. 3D shows that three sides of thecommon-auxiliary electrode 15 are exposed.

Storage electrode 43 forms storage capacitor by overlapping gate busline 1. Although not shown in the figures, the storage electrode 43 mayoverlap the common-auxiliary electrode 15.

FIGS. 3E, 3G show that passivation layer 37 includes SiN_(x) or SiO_(x)and FIGS. 3F, 3H show that passivation layer 37 includes BCB or acrylicresin in the LCD. Also, FIGS. 3E, 3F show that dielectric frame 53 isformed on the common electrode 17, and FIGS. 3G, 3H show that electricfield inducing window 51 is formed in the common electrode 17.

FIG. 4A is a plan view of the multi-domain liquid crystal display deviceaccording to the third embodiment of the present invention, and FIGS. 4Band 4C, 4D, 4E, 4F are sectional views taken along the lines V-V′ andVI-VI′ in FIG. 4A.

In the multi-domain LCD of the present invention, a part of upper-downpixels is formed on common-auxiliary electrode 15 that include a storageelectrode 43. The aperture ratio is largely improved as compared to theLCD in FIG. 2.

Moreover, the pixel electrode 13 overlaps common-auxiliary electrode 15,the light shielding layer 25 overlaps the common-auxiliary electrode 15,and the storage electrode 43 forms a storage capacitor withcommon-auxiliary electrode 15. FIGS. 4C, 4D show that dielectric frame53 is formed on the common electrode 17, and FIGS. 4E, 4F show thatelectric field inducing window 51 is formed in the common electrode 17.Also, FIGS. 4D, 4F show that the light shield layer 25 is formed only onthe thin film transistor.

FIGS. 5A and 5B are plan views of the multi-domain liquid crystaldisplay devices according to the fourth embodiment of the presentinvention, and FIGS. 5C and 5D are sectional views taken along the lineVII-VII′ in FIG. 5B.

The multi-domain LCD has the same structure as in the third embodimentof the present invention except as follows.

Pixel electrode 13 does not overlap common-auxiliary electrode 15, andthe light shielding layer 25 overlaps the pixel electrode 13. At thistime, a portion of the gate insulator 35 and passivation layer 37 on thecommon-auxiliary electrode 15 are removed, which intensifies theelectric field of common-auxiliary electrode 15 that is applied to thepixel electrode 13 (refer to FIG. 5B).

FIG. 5C shows a portion of the gate insulator 35 and passivation layer37 that are removed to expose a part of the common-auxiliary electrode15, and the FIG. 5D shows that three sides of the common-auxiliaryelectrode 15 are exposed.

FIG. 6A is a plan view of the multi-domain liquid crystal display deviceaccording to the fifth embodiment of the present invention, and FIG. 6Bis a sectional view taken along the line VIII-VIII′ in FIG. 6A.

FIG. 7 is a plan view of the multi-domain liquid crystal display deviceaccording to the sixth embodiment of the present invention.

In the multi-domain LCD of the present invention, a part of upper-downpixels is formed on common-auxiliary electrode 15 that include a commonstorage electrode 43. The aperture ratio is largely improved as comparedto the LCD in FIG. 6.

In the multi-domain LCD of the present invention, the aperture ratio isenhanced by an optimum structure design of a “n-line” thin filmtransistor (U.S. Pat. No. 5,694,185) so as to reduce power consumption,increase luminance, and lower reflection, thus improving contrast ratio.Aperture ratio is increased by forming the TFT above the gate line andproviding a “n-line” TFT. The parasitic capacitor, occurring between thegate bus line and the drain electrode, can be reduced when a TFT havingthe same channel length as the symmetrical TFT structure is manufactureddue to effect of channel length extension.

FIGS. 8A to 8G are plan views showing the various electric fieldinducing windows 51 and dielectric frames 53 according to theembodiments of the present invention.

The multi-domain LCD of the present invention has a dielectric frame 53on the pixel electrode and/or common electrode, or an electric fieldinducing window 51 like a hole or slit in the pixel electrode,passivation layer, gate insulator, color filter layer, and/or commonelectrode by patterning, thereby electric field distortion effect andmulti-domain are obtained.

That is, from forming electric field inducing window 51 or dielectricframe 53, the multi-domain is obtained by dividing each pixel into fourdomains such as in a “+”, “×”, or “double Y” shape, or dividing eachpixel horizontally, vertically, and/or diagonally, and differentlyalignment-treating or forming alignment directions on each domain and oneach substrate.

Furthermore, in multi-domain LCD of the present invention, an alignmentlayer(not shown in the figure) is formed over the whole first and/orsecond substrates. The alignment layer includes a material such aspolyamide or polyimide based materials, PVA (polyvinylalcohol), polyamicacid or SiO₂. When rubbing is used to determine an alignment direction,it should be possible to apply any material suitable for the rubbingtreatment.

Moreover, it is possible to form the alignment layer with aphotosensitive material such as PVCN (polyvinylcinnamate), PSCN(polysiloxanecinnamate), and CelCN (cellulosecinnamate) based materials.Any material suitable for the photo-aligning treatment may be used.Irradiating light once on the alignment layer determines the alignmentor pretilt direction and the pretilt angle. The light used in thephoto-alignment is preferably a light in a range of ultraviolet light,and any of unpolarized light, linearly polarized light, and partiallypolarized light can be used.

In the rubbing or photo-alignment treatment, it is possible to apply oneor both of the first and second substrates, and to apply differentaligning-treatment on each substrate.

From the aligning-treatment, a multi-domain LCD is formed with at leasttwo domains, and LC molecules of the LC layer are aligned differentlyone another on each domain. That is, the multi-domain is obtained bydividing each pixel into four domains such as in a “+” or “×” shape, ordividing each pixel horizontally, vertically, and/or diagonally, anddifferently alignment-treating or forming alignment directions on eachdomain and on each substrate.

It is possible to have at least one domain of the divided domainsunaligned. It is also possible to have all domains unaligned.

Consequently, since the multi-domain LCD of the present invention formsthe pixel electrode and the common-auxiliary electrode on the samelayer, a high voltage is not needed to raise the intensity of theelectric field applied between the two electrodes. Also, in the case ofconducting an alignment-treatment, a high response time and a stable LCstructure can be obtained by a pretilt angle and an anchoring energy.Moreover, the disclination is thus removed to thereby improve thebrightness.

It will be apparent to those skilled in the art that variousmodifications can be made in the liquid crystal display device of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. A multi-domain liquid crystal display devicecomprising: first and second substrates facing each other; a liquidcrystal layer between said first and second substrates; a plurality ofgate bus lines arranged in a first direction on said first substrate anda plurality of data bus lines arranged in a second direction on saidfirst substrate to define a pixel region, said pixel region beingdivided into at least two portions and liquid crystal molecules in saidliquid crystal layer in each portion being driven differently from eachother; a pixel electrode electrically charged through said data bus linein said pixel region; a common-auxiliary electrode surrounding saidpixel electrode on a same layer whereon said pixel electrode is formed;a gate insulator over said whole first substrate; a passivation layer onsaid gate insulator over said whole first substrate; a light shieldinglayer on said second substrate; a color filter layer on said lightshielding layer; a common electrode on said color filter layer; and analignment layer on at least one substrate between said first and secondsubstrates.
 2. The multi-domain liquid crystal display device accordingto claim 1, further comprising: a storage electrode connecting saidpixel electrode below said passivation layer and overlapping said gatebus line.
 3. The multi-domain liquid crystal display device according toclaim 1, wherein said light-shielding layer overlaps saidcommon-auxiliary electrode.
 4. The multi-domain liquid crystal displaydevice according to claims 1, wherein said common-auxiliary electrode iselectrically connect to said common electrode.
 5. The multi-domainliquid crystal display device according to claims 1, further comprising:a dielectric frame for distorting electric field on said commonelectrode.
 6. The multi-domain liquid crystal display device accordingto claims 1, wherein said pixel electrode has an electric field inducingwindow inside of itself.
 7. The multi-domain liquid crystal displaydevice according to claims 1, wherein said passivation layer has anelectric field inducing window inside of itself.
 8. The multi-domainliquid crystal display device according to claims 1, wherein said gateinsulator has an electric field inducing window inside of itself.
 9. Themulti-domain liquid crystal display device according to claims 1,wherein said common electrode has an electric field inducing windowinside of itself.
 10. The multi-domain liquid crystal display deviceaccording to claims 1, wherein said color filter has an electric fieldinducing window inside of itself.
 11. The multi-domain liquid crystaldisplay device according to claims 1, further comprising: an overcoatlayer on said color filter layer.
 12. The multi-domain liquid crystaldisplay device according to claims 1, wherein said overcoat layer has anelectric field inducing window inside of itself.
 13. The multi-domainliquid crystal display device according to claims 1, wherein saidpassivation layer includes a material selected from the group consistingof BenzoCycloButene (BCB), acrylic resin, and polyimide compound. 14.The multi-domain liquid crystal display device according to claims 1,wherein said common-auxiliary electrode includes a material selectedfrom the group consisting of Indium Tin Oxide (ITO), aluminum,molybdenum, chromium, tantalum, titanium, and an alloy thereof.
 15. Themulti-domain liquid crystal display device according to claims 1,wherein said pixel electrode includes a material selected from the groupconsisting of Indium Tin Oxide (ITO), aluminum, and chromium.
 16. Themulti-domain liquid crystal display device according to claims 1,wherein said common electrode includes Indium Tin Oxide (ITO).
 17. Themulti-domain liquid crystal display device according to claims 1,wherein said alignment layer is divided into at least two portions,liquid crystal molecules in each portion being aligned differently fromeach other.
 18. The multi-domain liquid crystal display device accordingto claims 17, wherein all portions of said at least two portions of saidalignment layer are non-alignment-treated.
 19. The multi-domain liquidcrystal display device according to claims 1, wherein said liquidcrystal layer includes liquid crystal molecules having negativedielectric anisotropy.
 20. The multi-domain liquid crystal displaydevice according to claims 1, further comprising: a negative bi-axialfilm on at least one substrate.
 21. The multi-domain liquid crystaldisplay device according to claims 1, wherein said liquid crystal layerincludes chiral dopants.
 22. A multi-domain liquid crystal displaydevice comprising: first and second substrates facing each other; aliquid crystal layer between said first and second substrates; aplurality of gate bus lines arranged in a first direction on said firstsubstrate and a plurality of data bus lines arranged in a seconddirection on said first substrate to define a pixel region, said pixelregion being divided into at least two portions and liquid crystalmolecules in said liquid crystal layer in each portion being drivendifferently from each other; and a pixel electrode electrically chargedthrough said data bus line in said pixel region; and a common-auxiliaryelectrode surrounding said pixel electrode on a same layer whereon saidpixel electrode is formed.
 23. A multi-domain liquid crystal displaydevice comprising: first and second substrates facing each other; aliquid crystal layer between said first and second substrates; aplurality of gate bus lines arranged in a first direction on said firstsubstrate and a plurality of data bus lines arranged in a seconddirection on said first substrate to define a pixel region, said pixelregion being divided into at least two portions and liquid crystalmolecules in said liquid crystal layer in each portion being drivendifferently from each other; an n-line thin film transistor at acrossing area of said gate and data bus lines; a pixel electrodeelectrically charged through said data bus line in said pixel region;and a common-auxiliary electrode surrounding said pixel electrode on asame layer whereon said pixel electrode is formed; a gate insulator oversaid whole first substrate; a passivation layer on said gate insulatorover said whole first substrate; a light shielding layer on said secondsubstrate; a color filter layer on said light shielding layer; a commonelectrode on said color filter layer; and an alignment layer on at leastone substrate between said first and second substrates.